1. Field of the Invention
The present invention relates to a resin composition, and more particlularly, to a resin composition containing an internal release agent that facilitates releasing of molded resin products from molds.
2. Description of the Related Art
In general, when polyurethane resins are molded in a mold, external release agents such as waxes, metal soaps and the like are applied to the mold each time.
However, such a method is disadvantageous from the standpoint of productivity as compared with molding of thermoplastic resins where an external release agent is dispensable in the case of mass production of automotive parts such as bumpers, fenders and the like.
In order to solve the problems, the demand has been to develop internal release agents and resin compositions having a self-releasing property.
As resin compositions with self-releasability, Japanese Patent Application Laid-open No. 17359/1979 discloses a RIM (reaction injection molding) process in which aromatic diamine crosslinking agents more reactive with isocyanates are used in place of low molecular weight glycols which have been heretofore used as crosslinking agents.
Further, Japanese Patent Publication No. 56887/1988 discloses a RIM process where polyether polyamines containing terminal primary amino groups and aromatic amino groups more reactive with isocyanates are used in place of conventional high molecular weight polyether polyols.
U.S. Pat. No. 4,794,129 discloses a RIM process using a polyether polyimine containing terminal imino groups.
By employing the above-mentioned techniques, the releasing property has been improved, but such improvement is not sufficient for facilitating industrial production of large and complicated bumpers. Japanese PCT Publication No. 500418/1985 discloses a technique actually used in industrial production in which fatty acid metal salts dissolved in amines are used as internal release agents.
When fatty acid metal salts are used as internal release agents, the releasing property is good, but washing before coating is problematic. That is, if the fatty acid metal salt bleeding from the molded product is not sufficiently washed from the product, the fatty acid metal salt causes fish eyes and poor adhesiveness upon coating.
When washed with water, the fatty acid metal salt bleeding to the surface can not be washed sufficiently, and therefore, an acid washing method which needs many steps has been employed.
In view of the foregoing, development of a resin composition having both good releasing property and coating property has been demanded.
With respect to techniques of internal release agents other than fatty acid metal salts, Japanese Patent Publication Nos. 24997/1974 and 42092/1980 disclose that fatty acid ester compounds are used for producing urethane foam resin.
Japanese Patent Publication No. 18368/1983 discloses a process for producing foam resin in which there is used a prepolymer produced by reacting a fatty acid ester compound containing hydroxyl groups and/or carboxyl groups with an isocyanate compound.
In addition, Japanese Patent Publication No. 29453/1989 discloses a process for producing urethane or urethane/urea elastomers by RIM where a particular ester compound of ricinolic acid is used as an internal release agent.
Further, U.S. Pat. No. 4,868,224 discloses a process for producing urethane and/or urea elastomers by RIM where a particular fatty acid ester compound containing OH groups is reacted with an isocyanate and the product is used as a prepolymer containing 5-45% NCO.
U.S. Pat. No. 4,868,224 also describes that as another internal release agent, a known zinc salt of fatty acid may be used in combination with the internal release agent. By using these internal release agents or isocyanate compounds containing an internal release agent, an external release agent which is one drawback of thermosetting resins is avoided or the frequent use of an external release agent can be decreased and releasing from mold is good and moreover, the rejection rate caused by urethane residue and built-up of the releasing agent in the mold cavity and breaking upon releasing can be decreased.
Fatty acid ester compounds disclosed in Japanese Patent Publication Nos. 24997/1974, 42092/1980 and 18368/1988 exhibit somewhat of a releasing property when used for low density foam resins, but hardly exhibit any releasing property when used for producing high density RIM elastomers having densities of 0.8-1.2.
According to reaction injection molding (RIM), two types of highly reactive liquid streams are impinged and mixed, and injected into a mold cavity at a high speed. One type of the stream is a stream of a polyisocyanate or a derivative thereof usually called "A" component and the other type of the stream is an isocyanate-reactive stream usually composed of a polyol and/or polyamine reactant called "B" component.
When a known particular ester compound of ricinoleic acid (Japanese Patent Publication No. 29453/1989) is used in the polyol side, "B", according to the example as an internal release agent, there is a releasing effect, but since the molecular ends have secondary hydroxyl groups, the reaction velocity with isocyanates is slow, and strength upon releasing (hereinafter referred to as "green strength") and stiffness upon releasing (shape keeping property) are insufficient. Therefore, it is necessary to lengthen the curing time in the mold.
In the above-mentioned Japanese Patent Publication No. 29453/1989, it is described that even when the fatty acid ester compound is partly reacted with the isocyanate and used as "A", the same releasing property can be exhibited, but the storage stability of the prepolymer is not sufficient. Though there is a releasing effect, it is not better than that when the ester compound of ricinoleic acid is incorporated in the polyol side, "B". The green strength and stiffness upon releasing are not sufficient, and the internal release agent is not sufficiently effective for industrial production of bumpers having a large and complicated shape and the like.